It is not that simple to code. The basic assumption seems to be that every course only has one quiz. What if a course has 20 lessons and 10 quizzes and certificate requires a 100% on each lesson and 70% on each quiz in order for a student to generate it?
Basically all the above requests are for a 3rd option for a date. The request is to print date the student met all the dependencies to receive their certificate. Thus the code will have to pick the lastest date for any attempt from any dependent activity as defined in the Certificate setting. Way beyond this hacker.
A slightly simplier piece of code would be to create a "capstone activity" pulldown in certificate settings, that shows all activities. The teacher selects the course capstone activity and what ever the date of the last attempt is for that activity is what always prints.
I suspose some clever php bit of code would search the student's log for the last quiz entry in the course and use that date. A bit easier to code but still beyond me
Of course there is also the option to tell the student to generate their certificate immediately....because the date on the certificate counts and there is a deadline or some other story. It is easy to put this OFFICIAL WARNING in bold as a label resource just before the certificate. This is my choice because it requires no php code tweaks
Hope this gives you some ideas for modifing the certificate code. Please share your solution.